Method and apparatus for indicating D2D resource pool in wireless communication system

ABSTRACT

A method and apparatus for indicating a device-to-device (D2D) resource pool in a wireless communication system is provided. A user equipment (UE) selects one of a first D2D resource pool or a second D2D resource pool. The first D2D resource pool may be a preconfigured D2D resource pool, and the second D2D resource pool may be a D2D resource pool received from a cell. The UE transmits an indication of the selected D2D resource pool while performing a D2D operation based on the selected D2D resource pool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/004507, filed on May 6, 2015,which claims the benefit of U.S. Provisional Application No. 61/988,923,filed on May 6, 2014, the contents of which are all hereby incorporatedby reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for indicating adevice-to-device (D2D) resource pool in a wireless communication system.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Recently, there has been a surge of interest in supportingproximity-based services (ProSe). Proximity is determined (“a userequipment (UE) is in proximity of another UE”) when given proximitycriteria are fulfilled. This new interest is motivated by severalfactors driven largely by social networking applications, and thecrushing data demands on cellular spectrum, much of which is localizedtraffic, and the under-utilization of uplink frequency bands. 3GPP istargeting the availability of ProSe in LTE rel-12 to enable LTE become acompetitive broadband communication technology for public safetynetworks, used by first responders. Due to the legacy issues and budgetconstraints, current public safety networks are still mainly based onobsolete 2G technologies while commercial networks are rapidly migratingto LTE. This evolution gap and the desire for enhanced services have ledto global attempts to upgrade existing public safety networks. Comparedto commercial networks, public safety networks have much more stringentservice requirements (e.g., reliability and security) and also requiredirect communication, especially when cellular coverage fails or is notavailable. This essential direct mode feature is currently missing inLTE.

As a part of ProSe, device-to-device (D2D) operation between UEs hasbeen discussed. For D2D operation, D2D resources needs to be defined.Accordingly, a method for indicating a D2D resource pool may berequired.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for indicating adevice-to-device (D2D) resource pool in a wireless communication system.The present invention provides a method for transmitting a resource pooltype indication (RPTI) for indicating a D2D resource pool used for D2Doperation.

In an aspect, a method for indicating, by a user equipment (UE), adevice-to-device (D2D) resource pool in a wireless communication systemis provided. The method includes selecting one of a first D2D resourcepool or a second D2D resource pool, and transmitting an indication ofthe selected D2D resource pool while performing a D2D operation based onthe selected D2D resource pool.

In another aspect, a user equipment (UE) includes a memory, atransceiver, and a processor coupled to the memory and the transceiver,and configured to select one of a first D2D resource pool or a secondD2D resource pool, and control the transceiver to transmit an indicationof the selected D2D resource pool while performing a D2D operation basedon the selected D2D resource pool.

A D2D resource pool can be indicated efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows reference architecture for ProSe.

FIG. 7 shows an example of mapping between sidelink transport channelsand sidelink physical channels.

FIG. 8 shows an example of mapping between sidelink logical channels andsidelink transport channels for ProSe direct communication.

FIG. 9 shows an example of a group of UEs performing D2D communicationand moving around the cell boundary.

FIG. 10 shows an example of a method for indicating a D2D resource poolaccording to an embodiment of the present invention.

FIG. 11 shows an example of a method for indicating a D2D resource poolby a UE moving from in-cell coverage to out-of-cell coverage accordingto an embodiment of the present invention.

FIG. 12 shows an example of a method for indicating a D2D resource poolby a UE moving from out-of-cell coverage to in-cell coverage accordingto an embodiment of the present invention.

FIG. 13 shows an example of transmission of D2D control informationaccording to an embodiment of the present invention.

FIG. 14 shows a wireless communication system to implement an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a systemarchitecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may bepositioned at the end of the network and connected to an externalnetwork. For clarity, MME/S-GW 30 will be referred to herein simply as a“gateway,” but it is understood that this entity includes both the MMEand S-GW.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 areconnected to each other via an X2 interface. Neighboring eNBs may have ameshed network structure that has the X2 interface. A plurality of nodesmay be connected between the eNB 20 and the gateway 30 via an S1interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem. FIG. 4 shows a block diagram of a control plane protocol stackof an LTE system. Layers of a radio interface protocol between the UEand the E-UTRAN may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe open system interconnection (OSI) model that is well-known in thecommunication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Databetween the MAC layer and the PHY layer is transferred through thetransport channel. Between different PHY layers, i.e. between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet dataconvergence protocol (PDCP) layer belong to the L2. The MAC layerprovides services to the RLC layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides data transferservices on logical channels. The RLC layer supports the transmission ofdata with reliability. Meanwhile, a function of the RLC layer may beimplemented with a functional block inside the MAC layer. In this case,the RLC layer may not exist. The PDCP layer provides a function ofheader compression function that reduces unnecessary control informationsuch that data being transmitted by employing IP packets, such as IPv4or IPv6, can be efficiently transmitted over a radio interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers (RBs). The RB signifies aservice provided the L2 for data transmission between the UE andE-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid ARQ (HARQ). The PDCP layer (terminatedin the eNB on the network side) may perform the user plane functionssuch as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The RRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physicalchannel transfers signaling and data between PHY layer of the UE and eNBwith a radio resource. A physical channel consists of a plurality ofsubframes in time domain and a plurality of subcarriers in frequencydomain. One subframe, which is 1 ms, consists of a plurality of symbolsin the time domain. Specific symbol(s) of the subframe, such as thefirst symbol of the subframe, may be used for a physical downlinkcontrol channel (PDCCH). The PDCCH carries dynamic allocated resources,such as a physical resource block (PRB) and modulation and coding scheme(MCS).

A DL transport channel includes a broadcast channel (BCH) used fortransmitting system information, a paging channel (PCH) used for paginga UE, a downlink shared channel (DL-SCH) used for transmitting usertraffic or control signals, a multicast channel (MCH) used for multicastor broadcast service transmission. The DL-SCH supports HARQ, dynamiclink adaptation by varying the modulation, coding and transmit power,and both dynamic and semi-static resource allocation. The DL-SCH alsomay enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normallyused for initial access to a cell, a uplink shared channel (UL-SCH) fortransmitting user traffic or control signals, etc. The UL-SCH supportsHARQ and dynamic link adaptation by varying the transmit power andpotentially modulation and coding. The UL-SCH also may enable the use ofbeamforming.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting multimedia broadcast multicast services(MBMS) control information from the network to a UE. The DCCH is apoint-to-point bi-directional channel used by UEs having an RRCconnection that transmits dedicated control information between a UE andthe network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC idle state (RRC_IDLE) and anRRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform public land mobile network (PLMN)selection and cell re-selection. Also, in RRC_IDLE, no RRC context isstored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context inthe E-UTRAN, such that transmitting and/or receiving data to/from theeNB becomes possible. Also, the UE can report channel qualityinformation and feedback information to the eNB. In RRC_CONNECTED, theE-UTRAN knows the cell to which the UE belongs. Therefore, the networkcan transmit and/or receive data to/from UE, the network can controlmobility (handover and inter-radio access technologies (RAT) cell changeorder to GSM EDGE radio access network (GERAN) with network assistedcell change (NACC)) of the UE, and the network can perform cellmeasurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UEmonitors a paging signal at a specific paging occasion of every UEspecific paging DRX cycle. The paging occasion is a time interval duringwhich a paging signal is transmitted. The UE has its own pagingoccasion. A paging message is transmitted over all cells belonging tothe same tracking area. If the UE moves from one tracking area (TA) toanother TA, the UE will send a tracking area update (TAU) message to thenetwork to update its location.

Proximity-based services (ProSe) are described. It may be referred to3GPP TR 23.703 V1.0.0 (2013-12). ProSe may be a concept including adevice-to-device (D2D) communication. Hereinafter, “ProSe” may be usedby being mixed with “D2D”.

-   -   ProSe direct communication means a communication between two or        more UEs in proximity that are ProSe-enabled, by means of user        plane transmission using E-UTRA technology via a path not        traversing any network node. ProSe-enabled UE means a UE that        supports ProSe requirements and associated procedures. Unless        explicitly stated otherwise, a ProSe-enabled UE refers both to a        non-public safety UE and a public safety UE. ProSe-enabled        public safety UE means a ProSe-enabled UE that also supports        ProSe procedures and capabilities specific to public safety.        ProSe-enabled non-public safety UE means a UE that supports        ProSe procedures and but not capabilities specific to public        safety. ProSe direct discovery means a procedure employed by a        ProSe-enabled UE to discover other ProSe-enabled UEs in its        vicinity by using only the capabilities of the two UEs with 3GPP        LTE rel-12 technology. EPC-level ProSe discovery means a process        by which the EPC determines the proximity of two ProSe-enabled        UEs and informs them of their proximity. ProSe UE identity (ID)        is a unique identity allocated by evolved packet system (EPS)        which identifies the ProSe enabled UE. ProSe application ID is        an identity identifying application related information for the        ProSe enabled UE.

FIG. 6 shows reference architecture for ProSe. Referring to FIG. 6, thereference architecture for ProSe includes E-UTRAN, EPC, a plurality ofUEs having ProSe applications, ProSe application server, and ProSefunction. The EPC represents the E-UTRAN core network architecture. TheEPC includes entities such as MME, S-GW, P-GW, policy and charging rulesfunction (PCRF), home subscriber server (HSS), etc. The ProSeapplication servers are users of the ProSe capability for building theapplication functionality. In the public safety cases, they can bespecific agencies (PSAP), or in the commercial cases social media. Theseapplications rare defined outside the 3GPP architecture but there may bereference points towards 3GPP entities. The application server cancommunicate towards an application in the UE. Applications in the UE usethe ProSe capability for building the application functionality. Examplemay be for communication between members of public safety groups or forsocial media application that requests to find buddies in proximity.

The ProSe function in the network (as part of EPS) defined by 3GPP has areference point towards the ProSe application server, towards the EPCand the UE. The functionality may include at least one of followings,but not be restricted thereto.

-   -   Interworking via a reference point towards the 3rd party        applications    -   Authorization and configuration of the UE for discovery and        direct communication    -   Enable the functionality of the EPC level ProSe discovery    -   ProSe related new subscriber data and handling of data storage,        and also handling of ProSe identities    -   Security related functionality    -   Provide control towards the EPC for policy related functionality    -   Provide functionality for charging (via or outside of EPC, e.g.,        offline charging)

Reference points/interfaces in the reference architecture for ProSe aredescribed.

-   -   PC1: It is the reference point between the ProSe application in        the UE and in the ProSe application server. It is used to define        application level signaling requirements.    -   PC2: It is the reference point between the ProSe application        server and the ProSe function. It is used to define the        interaction between ProSe application server and ProSe        functionality provided by the 3GPP EPS via ProSe function. One        example may be for application data updates for a ProSe database        in the ProSe function. Another example may be data for use by        ProSe application server in interworking between 3GPP        functionality and application data, e.g., name translation.    -   PC3: It is the reference point between the UE and ProSe        function. It is used to define the interaction between UE and        ProSe function. An example may be to use for configuration for        ProSe discovery and communication.    -   PC4: It is the reference point between the EPC and ProSe        function. It is used to define the interaction between EPC and        ProSe function. Possible use cases may be when setting up a        one-to-one communication path between UEs or when validating        ProSe services (authorization) for session management or        mobility management in real time.    -   PC5: It is the reference point between UE to UE used for control        and user plane for discovery and communication, for relay and        one-to-one communication (between UEs directly and between UEs        over LTE-Uu).    -   PC6: This reference point may be used for functions such as        ProSe discovery between users subscribed to different PLMNs.    -   SGi: In addition to the relevant functions via SGi, it may be        used for application data and application level control        information exchange.

Sidelink is UE to UE interface for ProSe direct communication and ProSedirect discovery. Sidelink comprises ProSe direct discovery and ProSedirect communication between UEs. Sidelink uses uplink resources andphysical channel structure similar to uplink transmissions. Sidelinktransmission uses the same basic transmission scheme as the ULtransmission scheme. However, sidelink is limited to single clustertransmissions for all the sidelink physical channels. Further, sidelinkuses a 1 symbol gap at the end of each sidelink sub-frame.

FIG. 7 shows an example of mapping between sidelink transport channelsand sidelink physical channels. Referring to FIG. 7, a physical sidelinkdiscovery channel (PSDCH), which carries ProSe direct discovery messagefrom the UE, may be mapped to a sidelink discovery channel (SL-DCH). TheSL-DCH is characterized by:

-   -   fixed size, pre-defined format periodic broadcast transmission;    -   support for both UE autonomous resource selection and scheduled        resource allocation by eNB;    -   collision risk due to support of UE autonomous resource        selection; no collision when UE is allocated dedicated resources        by the eNB.

A physical sidelink shared channel (PSSCH), which carries data from a UEfor ProSe direct communication, may be mapped to a sidelink sharedchannel (SL-SCH). The SL-SCH is characterized by:

-   -   support for broadcast transmission;    -   support for both UE autonomous resource selection and scheduled        resource allocation by eNB;    -   collision risk due to support of UE autonomous resource        selection; no collision when UE is allocated dedicated resources        by the eNB;    -   support for HARQ combining, but no support for HARQ feedback;    -   support for dynamic link adaptation by varying the transmit        power, modulation and coding.

A physical sidelink broadcast channel (PSBCH), which carries system andsynchronization related information transmitted from the UE, may bemapped to a sidelink broadcast channel (SL-BCH). The SL-BCH ischaracterized by pre-defined transport format. A physical sidelinkcontrol channel (PSCCH) carries control from a UE for ProSe directcommunication.

FIG. 8 shows an example of mapping between sidelink logical channels andsidelink transport channels for ProSe direct communication. Referring toFIG. 8, the SL-BCH may be mapped to a sidelink broadcast control channel(SBCCH), which is a sidelink channel for broadcasting sidelink systeminformation from one UE to other UE(s). This channel is used only byProSe direct communication capable UEs. The SL-SCH may be mapped to asidelink traffic channel (STCH), which is a point-to-multipoint channel,for transfer of user information from one UE to other UEs. This channelis used only by ProSe direct communication capable UEs.

ProSe direct communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface. Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform ProSe directcommunication. The UE performs Prose direct communication on subframesdefined over the duration of sidelink control period. The sidelinkcontrol period is the period over which resources allocated in a cellfor sidelink control and sidelink data transmissions occur. Within thesidelink control period the UE sends a sidelink control followed bydata. Sidelink control indicates a layer 1 ID and characteristics of thetransmissions (e.g. MCS, location of the resource(s) over the durationof sidelink control period, timing alignment).

For D2D communication, all UEs, in mode 1 and mode 2, may be providedwith a resource pool (time and frequency) in which they attempt toreceive scheduling assignments. The mode 1 indicates a scheduled mode inwhich an eNB or relay node (RN) schedules the exact resources used forD2D communication. The mode 2 indicates an autonomous mode in which a UEselects its own resources from a resource pool for D2D communication. Inthe mode 1, a UE may request transmission resources from an eNB. The eNBmay schedule transmission resources for transmission of schedulingassignment(s) and data. The UE may send a scheduling request (dedicatedSR (D-SR) or random access (RA)) to the eNB followed by a buffer statusreport (BSR) based on which the eNB can determine that the UE intends toperform a D2D transmission as well as the required amount resources.Further, in the mode 1, the UE may need to be in RRC_CONNECTED in orderto transmit D2D communication. For the mode 2, UEs may be provided witha resource pool (time and frequency) from which they choose resourcesfor transmitting D2D communication. The eNB may control whether the UEmay apply the model or mode 2.

ProSe direct discovery is defined as the procedure used by the UEsupporting direct discovery to discover other UE(s) in its proximity,using E-UTRA direct radio signals via PC5. ProSe direct discovery issupported only when the UE is served by E-UTRAN.

For D2D discovery, the eNB may provide in system information block (SIB)a radio resource pool for discovery transmission and reception for type1 and a radio resource pool for discovery reception of type 2B. For thetype 1, a UE may autonomously select radio resources from the indicatedtype 1 transmission resource pool for discovery signal transmission. Fortype 2B, only an RRC_CONNECTED UE may request resources for transmissionof D2D discovery messages from the eNB via RRC. The eNB may assignresource via RRC. Radio resource may allocated by RRC as baseline.Receiving UEs may monitor both type 1 and type 2B discovery resources asauthorized. In the UE, the RRC may inform the discovery resource poolsto the MAC. The RRC may also inform allocated type 2B resource fortransmission to the MAC.

FIG. 9 shows an example of a group of UEs performing D2D communicationand moving around the cell boundary. Referring to FIG. 9, UE1 to UE4consists of a D2D group. UE1 transmits a D2D synchronization signal(D2DSS). UE2 transmits a D2D data. UE3 and UE4 receive the D2D data. UE1to UE3 are in the cell coverage. It is assumed that UE4 is the cellcoverage firstly, but now, UE4 is out of the cell coverage. D2D resourcepool for transmission and reception of D2D communication may be providedto UEs at a cell by e.g. SIB or dedicated signaling. Thus, a group ofUEs transmitting or receiving D2D communication in the cell coveragemaintain up-to-date system information carrying the D2D resource pool.

As described above, if some UEs, like UE4 in FIG. 9 above, in the D2Dgroup leave/lose the cell coverage, preconfigured D2D resource pool,rather than the D2D resource pool provided by the cell, may be applied.Hence, UEs of the group in the cell coverage may transmit and receiveD2D scheduling assignment (SA) based on the D2D resource pool providedby the cell, while UEs of the group out of the cell coverage maytransmit and receive D2D SA based on the preconfigured D2D resourcepool. That may cause UEs of the group to fail to receive the D2D SA,because when a UE out of the cell coverage may transmit D2D SA based onthe preconfigured D2D resource pool while other UEs may monitor D2D SAbased on the D2D resource pool provided by the cell.

In order to solve the problem described above, a method for indicating aD2D resource pool according to an embodiment of the present invention isdescribed hereinafter.

FIG. 10 shows an example of a method for indicating a D2D resource poolaccording to an embodiment of the present invention.

In step S100, the UE selects one of a first D2D resource pool or asecond D2D resource pool. The first D2D resource pool may be apreconfigured D2D resource pool, and the second D2D resource pool may bea D2D resource pool received from a cell. That is, the first D2Dresource pool may be the preconfigured D2D resource pool which isreceived via signaling of an upper layer than layer 2 (MAC/RLC/PDCP) andlayer 3 (RRC), while the second D2D resource pool may be the D2Dresource pool received from a cell, e.g. by SIB or by dedicatedsignaling. If the UE is out of the cell coverage or if valid D2Dresource pool is not available in the UE, the first D2D resource pool,i.e. the preconfigured D2D resource pool, may be selected. If the UE isin the cell coverage or if valid D2D resource pool is available in theUE, the second D2D resource pool, i.e. the D2D resource pool receivedfrom a cell, may be selected,

Alternatively, the first D2D resource pool may be directly received froma cell, while the second D2D resource pool may be received from anotherUE. In this case, the UE may select the first D2D resource pool receivedfrom the cell, between them. Alternatively, the first D2D resource poolmay be received from a first UE, while the second D2D resource pool maybe received from a second UE. If the UE is camping on a cell, the UE mayselect the same D2D resource pool received from the same cell betweenthem. The UE may select an earlier received D2D resource pool betweenthem or a recently received D2D resource pool between them.

In step S110, the UE transmits an indication of the selected D2Dresource pool while performing a D2D operation based on the selected D2Dresource pool. The D2D operation may include D2D communication and/orD2D discovery. Or, the D2D operation may include D2D transmission and/orD2D reception.

The indication may be a resource pool type indication (RPTI). Theindication may indicate whether the first D2D resource pool or thesecond D2D resource pool is used for the D2D operation. Morespecifically, the indication may indicate whether or not thepreconfigured D2D resource pool is used for ongoing D2D transmissionsand/or upcoming D2D transmissions. The indication may indicate whetheror not a D2D resource pool provided by a cell (e.g. by SIB or bydedicated signaling) is used for ongoing D2D transmissions and/orupcoming D2D transmissions. The indication may indicated whether thepreconfigured D2D resource pool is used or a D2D resource pool providedby a cell (e.g. by SIB or by dedicated signaling) is used for ongoingD2D transmissions and/or upcoming D2D transmissions.

Further, the indication may additionally indicate further information.The indication may indicate from which cell the selected D2D resourcepool is received. The indication may indicate on which frequency theselected D2D resource pool is received. The indication may indicate thatthe selected D2D resource pool is used for transmissions in D2Dcommunication. The indication may indicate that the selected D2Dresource pool is used for receptions in D2D communication. Theindication may indicate that the selected D2D resource pool is used fortransmissions in D2D discovery. The indication may indicate that theselected D2D resource pool is used for receptions in D2D discovery.

The indication may be periodically transmitted (possibly, during acertain time interval, e.g. several seconds).

-   -   The transmission of the indication may be initiated upon camping        on a cell, upon leaving a cell, upon receiving a D2D resource        pool (e.g. in system information) forwarded by another UE over        D2D, upon receiving a D2D resource pool (e.g. in system        information) from a cell or from the network, when the selected        D2D resource pool becomes invalid, e.g. due to expiry of        validity time, or when the selected D2D resource pool changes        either from the first D2D resource pool to the second D2D        resource pool or from the second D2D resource pool to the first        D2D resource pool.

The indication may be transmitted along with a D2D resource poolreceived (e.g. in system information) from a cell or the network (e.g.for forwarding SIB to neighboring UEs), or an indication of whether theUE is in the cell coverage or out of the cell coverage.

FIG. 11 shows an example of a method for indicating a D2D resource poolby a UE moving from in-cell coverage to out-of-cell coverage accordingto an embodiment of the present invention. In this embodiment, it isassumed that the UE has pre-configured SA resource pool for D2Dtransmission and D2D reception, e.g. via open mobile alliance (OMA)device management (DM), or signaling of an upper layer than accessstratum. Further, it is assumed that a first UE is a UE transmitting theD2DSS, a second UE is a UE transmitting the D2D data, and a third UE isa UE receiving the D2D data. The first/second/third UEs consist of a D2Dgroup.

In step S200, while a second UE is camping on a cell, the second UEreceives system information and then acquires cell ID of the cell, SAresource pool for D2D TX/RX, and UL/DL frequency of the cell from thereceived system information. Alternatively, the UE may acquire cell IDof the cell, SA resource pool for D2D TX/RX, and UL/DL frequency of thecell by a dedicated signaling from the cell.

In step S210, the second UE selects the acquired SA resource pool forD2D TX/RX, and so the second UE applies the SA resource pool for D2DTX/RX. Since the second UE is in the cell-coverage, the second UE mayselect the D2D resource pool received from the cell.

In step S220, the first UE transmits the D2DSS. Accordingly, the secondUE may synchronize to the D2DSS broadcast by the first UE.

In step S230, if the second UE transmits D2D data or D2DSS (e.g. ifthere is D2D data to be transmitted in its D2D buffer), the second UEtransmits RPTI. The RPTI may indicate that the second UE uses D2Dresource pool received from the cell (e.g. by SIB or by dedicatedsignaling) for ongoing D2D transmissions and/or upcoming D2Dtransmissions. The RPTI may also indicate from which cell the selectedD2D resource pool is received, and/or on which frequency the selectedD2D resource pool is received (e.g. UL/DL frequency of the cell).

In step S240, the second UE may forward system information (e.g. onlyincluding cell ID of the cell, SA resource pool for D2D TX/RX, and UL/DLfrequency of the cell) to other UEs in the D2D group.

In step S250, if other UE successfully receive the forwarded systeminformation, other UE transmits acknowledgement of the forwarded systeminformation. The acknowledgement may be transmitted via, e.g. a RRCmessage, L2 control information such as MAC control element (CE), or L1signaling in D2D SA. If the second UE receives the acknowledgement ofthe forwarded system information from all other UEs in the D2D group,the second UE may stop forwarding system information, assuming thatsecond UE knows the number of UEs in the D2D group.

In step S260, the second UE transmits D2D SA according to the recentlyselected SA resource pool for D2D TX. And further, the second UEtransmits D2D data according to D2D SA.

In step S270, if the second UE moves to out-of-cell coverage, when thereceived system information becomes invalid, e.g. after 3 hours, thesecond UE selects the pre-configured SA resource pool for D2D TX. Then,the second UE applies the pre-configured SA resource pool for D2D TX,after all D2D data scheduled by the SA based on the selected SA resourcepool are successfully transmitted.

-   -   In step S280, when the second UE applies pre-configured SA        resource pool for D2D TX, the second UE transmits RPTI        indicating that the second UE uses pre-configured resource pool        for ongoing D2D transmissions and/or upcoming D2D transmissions.

In step S290, the second UE transmits D2D SA according to the recentlyselected SA resource pool for D2D TX. And, the second UE transmits D2Ddata according to D2D SA.

FIG. 12 shows an example of a method for indicating a D2D resource poolby a UE moving from out-of-cell coverage to in-cell coverage accordingto an embodiment of the present invention. In this embodiment, it isassumed that the UE has pre-configured SA resource pool for D2Dtransmission and D2D reception, e.g. via OMA DM, or signaling of anupper layer than access stratum. Further, it is assumed that a first UEis a UE transmitting the D2DSS, a second UE is a UE transmitting the D2Ddata, and a third UE is a UE receiving the D2D data. Thefirst/second/third UEs consist of a D2D group.

In step S300, for D2D transmissions, while the second UE is out of thecell coverage, if there is no valid system information, the second UEselects the pre-configured SA resource pool for D2D TX. Then, the secondUE applies the pre-configured SA resource pool for D2D TX (possibly,after all D2D data scheduled by the SA based on the selected SA resourcepool are successfully transmitted).

In step S310, the first UE transmits the D2DSS. Accordingly, the secondUE may synchronize to the D2DSS broadcast by the first UE.

In step S320, when the second UE applies the pre-configured SA resourcepool for D2D TX, the second UE transmits RPTI indicating that the secondUE uses the pre-configured resource pool for ongoing D2D transmissionsand/or upcoming D2D transmissions.

In step S330, the second UE transmits D2D SA according to the recentlyselected SA resource pool for D2D TX. And, the second UE transmits D2Ddata according to D2D SA.

The first UE moves from out-of-cell coverage to in-cell coverage. Instep S340, the first UE transmits the D2DSS. Upon moving fromout-of-cell coverage to in-cell coverage, in step S350, the first UE mayreceive SIB including cell ID of the cell, SA resource pool for D2DTX/RX, and UL/DL frequency of the cell. In step S351, the first UE mayforward the received SIB to other UEs in the D2D group. If the second UEsuccessfully receives the forwarded SIB, in step S352, the second UE maytransmit the acknowledgement of the received SIB.

Alternatively, the second UE may enter the cell coverage, and then, instep S353, the second UE may receive SIB including cell ID of the cell,SA resource pool for D2D TX/RX, and UL/DL frequency of the cell. Thesecond UE may forward the received SIB to other UEs in the D2D group.

In step S360, the second UE selects the SA resource pool for D2D TXwhich is forwarded from another UE in the D2D group, in step S351described above, or directly received from a cell, in step S353described above. Then, the second UE applies the SA resource pool forD2D TX, after all D2D data scheduled based on pre-configured SA ResourcePool for D2D TX are successfully transmitted.

If the second UE transmits D2D data (e.g. if there is D2D data to betransmitted in its D2D buffer), in step S370, the second UE transmitsRPTI. The RPTI may indicate that the second UE uses D2D resource poolreceived from the cell (e.g. by SIB, by dedicated signaling or byforwarding from another UE) for ongoing D2D transmissions and/orupcoming D2D transmissions. The RPTI may also indicate from which cellthe selected D2D resource pool is received, and/or on which frequencythe selected D2D resource pool is received (e.g. UL/DL frequency of thecell).

In step S380, the second UE transmits D2D SA according to the recentlyselected SA resource pool for D2D TX. And, the second UE transmits D2Ddata according to D2D SA.

FIG. 13 shows an example of transmission of D2D control informationaccording to an embodiment of the present invention. D2D controlinformation, such as a RPTI or forwarded SIB, etc., may be transmittedover direct interface between UEs. D2D control information may berepeated periodically according to the D2D repetition period. D2Dcontrol information may be transmitted from a UE transmitting D2DSS or aUE performing D2D transmission in D2D communication. D2D controlinformation may change according to the D2D modification period. Namely,D2D control information may change only at the boundary of the D2Dmodification period. SA transmissions may occur periodically accordingto the SA period. SA may be re-transmitted in MAC or physical layerwithin one SA period. In FIG. 13, SA re-transmissions are not shown.

FIG. 14 shows a wireless communication system to implement an embodimentof the present invention.

An eNB 800 may include a processor 810, a memory 820 and a transceiver830. The processor 810 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 810. The memory 820 is operatively coupled with the processor810 and stores a variety of information to operate the processor 810.The transceiver 830 is operatively coupled with the processor 810, andtransmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a transceiver930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The transceiver 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method for a first user equipment (UE) in awireless communication system, the method comprising: configuring afirst device-to-device (D2D) resource pool, which is used out of acoverage of a cell; receiving, from the cell, information on a secondD2D resource pool, which is used in the coverage of the cell, whereinthe second D2D resource pool is updated periodically; selecting thesecond D2D resource pool while the first UE is located in the coverageof the cell; transmitting D2D data to a second UE based on the secondD2D resource pool, wherein the second UE is located in coverage of thecell; upon moving out of the coverage of the cell, selecting the firstD2D resource pool; upon selecting the first D2D resource pool,transmitting a resource pool type indication (RPTI) via the second D2Dresource pool to the second UE which is still located in coverage of thecell, wherein the RPTI indicates that upcoming D2D data will betransmitted on the first D2D resource pool; and transmitting theupcoming D2D data based on the first D2D resource pool to the second UE,wherein the RPTI further indicates a cell identity (ID) which informsfrom which cell the second D2D resource pool is received.
 2. The methodof claim 1, wherein the RPTI further indicates on which frequency thesecond D2D resource pool is received.
 3. The method of claim 1, whereinthe RPTI is transmitted periodically.
 4. A user equipment (UE)comprising: a memory; a transceiver; and a processor coupled to thememory and the transceiver, and configured to: configure a firstdevice-to-device (D2D) resource pool, which is used out of a coverage ofa cell; control the transceiver to receive, from the cell, informationon a second D2D resource pool, which is used in the coverage of thecell, wherein the second D2D resource pool is updated periodically;select the second D2D resource pool while the UE is located in thecoverage of the cell; control the transceiver to transmit D2D data to asecond UE based on the second D2D resource pool, wherein the second UEis located in coverage of the cell; upon moving out of the coverage ofthe cell, selecting the first D2D resource pool; upon selecting thefirst D2D resource pool, control the transceiver to transmit a resourcepool type indication (RPTI) via the second D2D resource pool to thesecond UE which is still located in coverage of the cell, wherein theRPTI indicates that upcoming D2D data will be transmitted on the firstD2D resource pool; and control the transceiver to transmit the upcomingD2D data based on the first D2D resource pool to the second UE, whereinthe RPTI further indicates a cell identity (ID) which informs from whichcell the second D2D resource pool is received.